1. Field of the Invention
This invention relates to a high temperature furnace that is capable of heating products to temperatures on the order of 3000.degree. F. and higher such as is necessary in fusing silica.
2. Description of the Prior Art
Certain materials must be heated to a relatively high temperature before fusing or melting occurs. For example, crystalline silica must be heated to a temperature between 3100.degree. and 3200.degree. F. before fusing of the silica takes place to form an amorphous material. Since very few materials remain solid without decomposition at these elevated temperatures, it is difficult to construct furnaces capable of heating materials to these high temperatures.
One type of prior art furnace utilized to heat materials to the temperature range involved includes an elongated carbon housing of a tubular shape with electrical terminals at each of its ends. At a mid-point intermediate the electrical terminals, the tubular wall thickness of the housing necks down so as to provide a location of greater resistance where relatively high temperatures are generated. There is a limit to the voltage that can be applied to this type of furnace, i.e., on the order of 4 or 5 volts, and thus relatively high currents on the order of 2000 amps or more must be used to develop the heat input required.
Another type of prior art furnace for generating high temperatures utilizes electrically conductive graphite elements which are threaded to provide nut and bolt connections that establish an electric flow path through the chamber of the furnace to be heated. U.S. Pat. Nos. 2,472,612 and 3,004,090 disclose furnaces of this type.
Also, U.S. Pat. No. 3,567,196 discloses a conveyor for transporting products to be heated through a high temperature furnace.